The invention relates generally to the area of electro-discharge machining (EDM) apparatus and specifically provides a tool feed mechanism control circuit to control the magnitude of the machining gap in response to the electrical conditions therein.
The prior art discloses various types of tool feed mechanism control circuits. One control circuit measures the ionization voltage across the machining gap during each discharge and uses this measurement to control the feed mechanism. Other systems detect the average discharge voltage as a control variable. Further prior art discloses the detection of discharge current during a machining discharge which is combined with a measurement of the discharge voltage to generate control signals. The control signals may be generated in either analog or digital form to control either analog or digital feed mechanism. Other prior art discloses many additional supplementary control circuits. The most prevalent of these is the detection of the number of actual machining discharges relative to the number of machining pulses applied to the machining gap. As the ratio of discharges to machining pulses decreases, the servomechanism is controlled correspondingly.
Although many of these systems provide an adequate control under normal machining conditions, applicants have devised a tool feed mechanism control circuit which is very sensitive to abnormal conditions in the machining gap. Applicants disclose the use of a low power pulse during the ON time prior to the application of a machining. The low power pulse produces a gap voltage signal which is very sensitive to changes in electrical conditions in the machining gap. Consequently, by using the gap voltage signal produced by a low power pulse as a sensing mechanism, the changes in the machining gap which normally lead to unsatisfactory machining discharges can be detected. Therefore, appropriate changes can be made at an earlier time than if only the variables present during a machining discharge are measured.